Consumer surveys are based upon samples of
selected respondents, rather than censuses of entire populations. A census
is prohibitively expensive for the sole purpose of obtaining consumer data, and
a properly designed and executed sample survey can provide results with
sufficient accuracy. There
are many different ways of selecting samples, some good, some not so good and
some bad based upon different considerations. Generally speaking, the
following objectives are considered desirable:

The sample should be cost-efficient

The sample should be representative of the population
universe

The sample should be objectively chosen

The sample should be verifiable by an auditor

In a previous article, we
provided a description of how to draw a probability sample. The process is
divided into a multistage sampling process, such that representativeness is
ensured while being variable at each stage. In this article, we will
discuss what happens during a particular sampling stage --- namely, the field cluster, which is the sample location at which a group of interviews are
conducted.

Typically, the interviewer is provided with a street map of the field location. A random point (e.g.
the third house west starting from the southeast corner of a
street block) is assigned to
each block to indicated where the interviewer should start contacting households. In
addition, the interviewer is given a specific path (e.g. traverse
the block by going east, then south, then west, then north) to follow in order to complete the assigned
number of attempts (or interviews). If the bookkeeping is done correctly, an
auditor or supervisor should to able to retrace the steps of the interviewer to
verify that the work was performed according to the instructions.

Abstractly, when such a procedure is prescribed, one
conjures up the image of square city blocks. It is true that most of the
towns founded by the Spaniards in Latin America followed a grid layout, with
straight streets crossing one another at ninety-degree right angles. In
some cases, these streets are given names that are just sequential numbers (e.g.
calle 1, 2, 3 ... in the north-south direction and carrera 1, 2, 3
in the east-west direction). Such towns have a main square, around which
the main administrative and religious buildings are situated, and the rest of
the town expands outwards following the grid layout. The above map of a
section of Caracas (Venezuela) is an example of square city blocks. When
such is the case, the standard interviewer's instructions can be executed
without ambiguity.

Unfortunately, life is never simple. When the Spanish
conquistador Diego de Losada founded the town of Santiago de León de Caracas on July 25, 1567, he
envisioned a
small provincial town that lied in a narrow east-west valley that was sunny, dry, warm, with refreshing
breezes and few mosquitoes. Caracas was not a major
Spanish viceroyalty for it had neither mineral wealth nor strategic value at the
time. For the first three centuries, Caracas was indeed a small, quiet, provincial
outpost. As history would have it, the country of Venezuela came into being
with Caracas serving as the capital. Instead of metal gold, Venezuela
would be blessed with black gold --- petroleum, and Caracas would grow into a
city with millions of inhabitants. In the last 50 years, the population of
Caracas had grown from half a million to over four million.

Certainly, part of that growth was accommodated by the many glitzy steel-and-glass modern skyscrapers in
the central area. But the narrow valley of Diego de Losada could not be overbuilt to accommodate
the exploding residential needs. Buildings began to appear on the hillsides,
growing upwards to
form entire barrios. Now, instead of the square city blocks, there are serpentine
paths following the hillscape and criss-crossing the hillsides. The
following map of another area in Caracas is an example of these serpentine
paths.

The standard instructions about how to handle square city
blocks are not applicable to these serpentine paths. For example, what is
the meaning of a street corner? And how can you turn left if there is
nothing but a cliff ledge at the end of the road? Of course, this does not
mean that probabilility samples are impossible to execute under these
circumstances. Rather, we are only making the point that standard
procedures have to be adapted to local conditions. It is just that special
instructions have to written, and interviewers have to undergo additional
training.

In the following, we show some photos that were taken of hillside
barrios in Caracas. From a distance, some of these buildings
resemble a house of cards, with one stacked on top of another. In most
cases, there is no vehicular access to these houses and one must resort to
walking up the serpentine paths that weave back and forth, inching upwards ever
so slowly.

Elsewhere in Latin America (notably, in Rio de Janeiro), the hillside dwellings are
often squatter homes built from cardboards and tin sheets. But it should be clear from these
photos that this is not uniformly so in Caracas. Some hillsides are
covered with shabby ranchitos that are made of brick and mortar, while other hillsides are bustling with
newly constructed modern urbanizaciones.